190 



THE LEAF 



se])arati()n has occurred, and the lamina has become divided into a 

 number of distinct secondary bhides (Figs. 54S, .554, etc.). Leaves of 

 this kind are called Compound, and their divisions, Leaflets. 



If the leaflets are themselves compound, the leaf is Decompound. 

 Decompound leaves are spoken of as once compound, twice compound, 

 etc., according to the number of successive divisions. Leaflets may be 

 distinguished from leaves by the fact that no buds are found in their 

 axils. Leaflets are subject to the ai)i)lication of the same descriptive 

 terminology as leaves. 



Leaflets of the first division are called Pinnae, those of subsequent 

 divisions, Pinnules. 



The continuation of the petiole passing up among the leaflets, that is 

 the midrib of the compound leaf, is the rachis (6, Fig. 475). 



Fig. 547. Palmately compound leaf {Aesculus). 548. Palmately trifoliolate leaf (Trifolium) . 549. 

 Pinnately trifoliolate leaf (.Lespedeza) . 550 and 551. Unifoliolate compound leaves of orange. 



When, as in Fig. 548, the compound leaf has no rachis, its division 

 being on the same plan as the lobing of the palmatifid leaf, it is Palmate, 

 or Palmately compound. When the rachis does exist, corresponding to 

 the pinnatifid type (Figs. 549 and 554), the leaf is Pinnate, or Pinnately 

 Compound. 



Before proceeding to define the distinct forms of the two classes, we 

 note that it is not always possible to identify them with readiness. For 

 example, the ancestral form of the leaf of the orange was pinnate, but 

 at the present time we find that only the terminal leaflet remains, 

 there being usually at the base more or less of an indication of the two 

 lateral leaflets which once existed (Figs. 550 and 551). Such a leaf 

 cannot, therefore, be properly designated as simple, and we designate 

 it as a Unifoliolate compound leaf. 



Compound leaves with three leaflets, usually designated as Trifolio- 

 late, frequently give us considerable difficulty in determining whether 



